This invention relates to anionic borate ligands, and bis(phosphino) and (bis(amino) borate ligands in particular. The invention further relates to zwitterionic complexes formed between anionic borate ligands and metals, such complexes finding utility in numerous stoichiometric and catalytic applications.
Cationic, coordinatively unsaturated metal centers have played a critical role in the development of organometallic catalysis, and exhibit a wide range of both stoichiometric and catalytic transformations. Such species are frequently generated by methide abstraction with a strong Lewis acid, and they can also be generated by protonation with an acid whose conjugate base is noncoordinating or weakly coordinating.
These cationic metal centers are amongst the most widely studied systems in organometallic research. Industrially important polymerization reactions often undergo key intermediary steps at cationic metal centers. With respect to transformations important to organic synthesis, cationic late metal fragments enjoy widespread use in Cxe2x80x94E bond forming processes, where E is C, N, O, S, Si, H, and so forth. Moreover, cationic metal centers are promising candidates for the ultimate goal of selective activation and functionalization of light hydrocarbon substrates.
However, in spite of the advances in the art, there continues to be a need for improved methods of mediating reaction chemistry. The present invention addresses those needs by a unique approach to the chemistry of cationic species whereby charge neutral zwitterions incorporating a partially insulated borate counter-anion are used to mediate reaction chemistry related to their discrete cationic relatives. A review of the use of zwitterions in organometallic chemistry is described in Chauvin et al., Eur. J. Inorg. Chem. 577 (2000). Aside from the advantage of eliminating the need for a cocatalyst, there are several significant reactivity differences between the zwitterionic complex of the invention and traditionally cationic systems due to (i) differences in their relative electrophilicities, (ii) differences in donor ligand lability, and (iii) reduced or completely eliminated ion-pairing effects in the zwitterionic systems by comparison to their cationic counterparts. Further, solvents that dissolve ionic compounds almost always have polar, hence coordinating functional groups that can attenuate their reactivity. In principle, the zwitterionic complex of the invention will provide access to the chemistry of cationic metal centers in relatively non-polar hydrocarbon media.
One aspect of the invention relates to compound having the formula: 
wherein: R1 and R2 are independently selected from the group consisting of alkyl and aryl; Y is selected from the group consisting of P and N; and R3, R4, R5 and R6 are independently selected from the group consisting of alkyl and aryl.
Another aspect of the invention pertains to a zwitterionic complex of the formula: 
wherein: R1 and R2 are independently selected from the group consisting of alkyl and aryl; Y is selected from the group consisting of P and N; R3, R4, R5 and R6 are independently selected from the group consisting of alkyl and aryl; Z is a metal; and R7 and R8 are independently selected from the group consisting of halo, pseudo-halo, alkyl, aryl and mono or bidentate, displaceable neutral donor ligands.
Another aspect of the invention pertains to a zwitterionic complex of the formula III: 
wherein: R1 and R2 are independently selected from the group consisting of alkyl and aryl; Y is selected from the group consisting of P and N; R3, R4, R5 and R6 are independently selected from the group consisting of alkyl and aryl; Z is a metal; and R7 is selected from the group consisting of halo, pseudo-halo, alkyl, aryl and mono or bidentate, displaceable neutral donor ligands.
Yet another aspect of the invention relates to a method of catalyzing a reaction wherein transformation of a robust sigma bond in an organic compound is required, comprising: a) contacting the organic compound with i) an organic or inorganic reagent, and ii) a zwifferionic complex of an anionic borate ligand having the formula: 
and a metal compound; wherein: R1 and R2 are independently selected from the group consisting of alkyl and aryl; Y is selected from the group consisting of P and N; and R3, R4, R5 and R6 are independently selected from the group consisting of alkyl and aryl; and b) producing an organic compound having a transformed robust sigma bond.